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Transition metal-based layered compounds with van der Waals gaps between the structural layers are a rich source of magnetic materials for spintronic applications. Bulk crystals can be cleaved, providing high-quality two-dimensional nanomaterials, which are promising for the manipulation of spins in spintronic devices and low power quantum logic interfaces. The layered van der Waals telluride Fe

A synthetic approach to a novel type of phosphonium and mixed phosphonium-iodonium ylides containing a conformationally fixed phosphonium fragment is developed. New representatives of these families of chemical compounds based on cyclic phenoxaphosphinine were synthesized. One compound was structurally characterized by single-crystal X-ray diffraction. Based on the 1H NMR data, one can state that phosphonium ylide exists in solution in the form of two geometric isomers even at room temperature. This is indicative of pronounced double-bond character of the bond between the ylide carbon atom and the stabilizing carbomethoxy group.

Hexamethylenetetramine (HMT) was used as a strong base for the preparation of new hybride iodobismuthates, (HMTH)2BiI5·(CH3)2C═O (1) and (HMTH)2BiI5 (2). They crystallize in the orthorhombic system...

The structure of synthetic tennantite Cu12As4S13was investigated at various temperatures in the 90–293 K range. It crystallizes in space group I{\overline 4}3m. No structural transformation was observed in this temperature range. The structures were refined in anharmonic approximation for atomic displacements and electron density maps were refined using the maximum entropy method. Both approaches indicate a noticeable static disorder of the copper atoms in the triangular sulfur coordination and neighbouring site at high temperatures, whereas these split copper sites are well defined at lower temperatures. One particle potential is used to describe the behaviour of atoms at these copper sites. Such behaviour may be the structural reason for changes in magnetic properties.

A treatment of the ligands, 3‑(2‑methylbutyl)‑5‑pyridylmethylene-substituted 2‑thio‑3,5‑dihydro‑4Н‑imidazole‑4‑one (L) with CuCl2·2H2O in MeOH/CH2Cl2 or Cu(acac)2 in MeOH/CH2Cl2 affords to binuclear complexes with the [L-H]2Cu+1.5Cu+1.5Cl or [L-H]2CuICuI composition, respectively. X-ray crystallography demonstrated close Cu-Cu interaction for the first complex and the absence of Cu Cu bonding for the second one.

New hybrid iodobismuthates (C12H18N2)(BiI4)2 (1, C12H18N2 is N,N´-bis(1- methylethylidene)-1,4-benzоdiammonium dication) and (C6H4(NH3)2) [Bi2I8•2DMSO]•4DMSO (2, C6H4(NH3)2 is p-phenylenediammonium dication) were synthesized and their crystal structures were established. Compound 1 crystallizes in the space group P21/n, a = 7.632(4), b = 13.471(6), c = 14.556(5) A, β = 93.57(4)°; compound 2 crystallizes in the space group P $$\overline 1 $$ , a = 9.208(4), b = 12.203(5), c = 13.600(5) A, α = 110.20(3)°, β = 97.28(4)°, γ = 110.04(4)°. In the crystal structure of compound 1, one-dimensional infinite BiI 4 – polyanions are linked into a three-dimensional structure by N,N'-bis(1-methylethylidene)- 1,4-benzоdiammonium dications through N–H…I and C–H…I hydrogen bonds. Compound 1 is stable up to 200 °С, optical studies showed that it has a band gap of 2.15 eV. The recrystallization of compound 1 from DMSO is accompanied by the transformation of chain BiI 4 – anions to binuclear [Bi2I8•2DMSO]2– anions, while the azomethine cation decomposes to form a p-phenylenediammonium dication.

We report the synthesis, crystal structures, and optical properties of two new compounds, K18Bi8I42(I2)0.5·14H2O (1) and (NH4)7Bi3I16(I2)0.5·4.5H2O (2), as well as the electronic structure of the latter. They crystallize in tetragonal space group P4/mmm with the unit cell parameters a = 12.974(1) and c = 20.821(3) A for 1 and a = 13.061(3) and c = 15.162(7) A for 2. Though 1 and 2 are not isomorphous, their crystal structures display the same structural organization; namely, the BiI6 octahedra are linked by I2 units to form disordered layers in 1 and perfectly ordered chains in 2. The I–I bond distances in the thus formed I–I–I–I linear links are not uniform; the central bond is only slightly longer than in a standalone I2 molecule, whereas the peripheral bonds are significantly shorter than longer bonds typical for various polyiodides, which is confirmed by Raman spectroscopy. The analysis of the electronic structure shows that the atoms forming the I–I–I–I subunits transfer electron density from their o...

The crystal structures of 6-methyl-2-ethyl-3-hydroxypyridiniun nitrate (C8H12NO)NO3 (I) and fumarate (C8H12NO)2C4H2O4 (II) were solved and refined from X-ray single crystal diffraction data (CuKα, (I) a=4.6477(2), b=14.5906(9), c=14.5551(8) Å, β=99.100(4)°, space group P21 /c, Z=4, Rp /Rwp =0.033/0.047; (II) a=8.8293(3), b=13.4268(5), c=8.3893(3) Å, β=96.303(3)°, space group P21/c, Z=2, Rp /Rwp= 0.034/0.049). Both structures are built of infinite chains along ac diagonal of the unit cells formed by hydrogen bonding between the hydroxypyridium cation and the corresponding anion. Each fumarate anion is linked to four hydroxypyridium cations while nitrate anion is connected with two hydroxypyridium cations only leaving one oxygen atom in the nitrogen group isolated.

NASICON-type lithium-vanadium phosphate (Li 3 V 2 (PO 4 ) 3 ) based electrodes capable to provide extremely fast lithium transport properties were studied by a combination of structure, morphology and surface characterization methods: X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), laser diffraction particle size distribution (PSD), as well as electrochemical methods: potentiostatic (PITT) and galvanostatic (GITT) intermittent titration techniques, electrochemical impedance spectroscopy (EIS), and constant current chronopotentiometry. Significant differences in the kinetics of reversible lithium intercalation depending on the lithiation stage were found: lithium diffusion coefficients, found from the PITT, GITT and EIS data, demonstrate an abrupt drop by 2–3 orders of magnitude (from 10 −9 to 10 −12 cm 2 s −1 ) in the 4.3–4.4 V potential range vs Li/Li + , which is attributed to the LiV 2 (PO 4 ) 3 ↔ V 2 (PO 4 ) 3 phase transition. The electrochemical extraction/insertion of two lithium equivalents can occur at ultra-high rates (up to 320C) from/into structurally more accessible Li2 and Li3 sites, while the de/intercalation of the third lithium equivalent from/into the Li1 position is supposedly hindered kinetically. To analyze the electrochemical data, specially developed theoretical models were used, which take into account geometry and phase configuration of the diffusion space, as well as the properties of the phase boundary interfaces. Morphology and size distribution parameters, essential for mathematical processing of the electrochemical data, were obtained by SEM, PSD and BET methods.

A treatment of the ligands, 3-benzyl-substituted 5-(pyridin-2-ylmethylidene)-2-thioxoimidazolidin-4-ones, with Cu(acac)2 in CH2Cl2 affords the mononuclear bis-ligand copper(II) complexes of the corresponding thiohydantoins.

The modification of Chan–Lam–Evans cross-coupling reaction for the selective Se-arylation of 2-selenohydantoins under base-free mild conditions via aryl boronic acids is described herein. This approach was used to synthesize novel 5-arylidene-3-substituted-2-(arylselanyl)-imidazoline-4-ones with high yields. The anticancer activity of the final compounds was evaluated in vitro against different cancer cells, and thus, the possibility of 5-arylidene-3-substituted-2-(arylselanyl)-imidazoline-4-ones successful application as cytotoxic agents was demonstrated.

The structure of synthetic tennantite Cu

Synthetic tennantite, Cu 12 As 4 S 13 , is the analogue of an abundant mineral that belongs to the tennantite-tetrahedrite group with a low lattice thermal conductivity. Combined data from high-quality X-ray diffraction, electron microscopy (STEM–HAADF), Raman spectroscopy, as well as DFT calculations are used to analyze the peculiarities of its structure stability and dynamics. Atomic displacement parameters (ADP) and low-energy optical phonon modes are discussed within the context of the structure variations and pecularities of the charge distribution. The latter indicates that the tennantite structure tends to conform to the covalent polar bonds and its charge distribution is significantly affected by the atomic shifts in Laves polyhedra. According to the DFT calculations, there is a population of stable model structures with varying shifts of copper atoms in Laves polyhedra, with total energies being very close (within 0.24 ​eV), which can explain the observed behavior of the ADP. A specially designed technique is used for the experimental analysis of the ADP that revealed Einstein characteristic temperatures in the tennantite structure to be in the range of 50–190 ​K, which is attributed to low-energy optical phonon modes.

A new phase Fe32+δGe33As2 (δ ≤ 0.136) was obtained by two-step synthesis from the elements. Fe32+δGe33As2 crystallizes in its own structure type (space group P6/mmm, Z = 1, a = 11.919(3) A, c = 7.558(4) A) that can be described as a recurrent two-dimensional intergrowth of two intermetallic structure types, MgFe6Ge6 and Co2Al5. Their blocks are represented by infinite columns in the structure. No visible structural changes were observed in the temperature range from 10 to 300 K. At 125 K, Fe32+δGe33As2 undergoes an antiferromagnetic-like transition, while above 150 K it shows a typical Curie–Weiss paramagnetic behavior. Below the transition temperature, a peculiar field-dependent magnetic susceptibility, that shows a significant increase of the susceptibility upon increasing the magnetic field, and a change in transport properties have been observed. Above 140 K, Fe32+δGe33As2 reveals a metallic behavior, in agreement with electronic structure calculation, while below this point the resistivity nonmonoton...

The preparation and properties of novel mixed arsonium–iodonium and sulfonium–iodonium ylides are reported. A series of substituted arsonium and sulfonium ylides was obtained by the nucleophilic substitution of iodonium groups in mixed ylides. A one-pot process, which included the nucleophilic substitution and silylation of arsonium–iodonium ylides with subsequent elimination of the silyl group and a Wittig olefination reaction, provided route to access Z-α,β-unsaturated haloketones.

The incommensurate modulated crystal structure of Bi2.27Sr1.73CuO6 + δ(2201) phase [a= 5.3874 (5),b= 5.3869 (4),c= 24.579 (3) Å; β = 90.01 (1)°,q= 0.2105 (3)a* + 0.538 (4)c*,Z= 4, the (3 + 1)-dimensional monoclinicA2/a(α0γ) group] has been refined withR= 0.041,wR= 0.052 from X-ray single-crystal data including up to third-order satellite reflections. The same structure has also been considered as incommensurate composite witha2= 2.437,b2= 5.387,c2= 24.614, β2= 93.06,q2= 0.4524a2*−0.243c2*and the (3 + 1)-dimensionalA2/m(α0γ)0sgroup for the second component. Both approaches give quite similar results. The structure possesses oxygen disorder in the oxygen-rich region of the BiO layer. An extra O atom is determined in the bridging position shifted ∼ 0.6 Å from BiO towards the SrO layer. Its presence is the cause of the tremendous increase of the bismuthU11atomic displacement parameter in ∼ 20% of the unit cells (t= −0.05–0.15). Vacancies are determined in the oxygen site of the SrO layer, which may result in the oxygen content variation with annealing at different oxygen pressures. The total refined oxygen content 6.18 (1) corresponds to the results of chemical analysis.

Four iodobismuthates, LiBiI4·5H2O (1), MgBi2I8·8H2O (2), MnBi2I8·8H2O (3), and KBiI4·H2O (4), were prepared by a facile solution route and revealed thermal stability in air up to 120 °C. Crystal structures of compounds 1-4 were solved by a single crystal X-ray diffraction method. 1: space group C2/c, a = 12.535(2), b = 16.0294(18), c = 7.6214(9) Å, β = 107.189(11)°, Z = 4, R = 0.029. 2: space group P21/c, a = 7.559(2), b = 13.1225(15), c = 13.927(4) Å, β = 97.14(3)°, Z = 2, R = 0.031. 3: space group P21/c, a = 7.606(3), b = 13.137(3), c = 14.026(5) Å, β = 97.14(3)°, Z = 2, R = 0.056. 4: space group P21/n, a = 7.9050(16), b = 7.7718(16), c = 18.233(4) Å, β = 97.45(3)°, Z = 4, R = 0.043. All solid state structures feature one-dimensional (BiI4)(-) anionic chains built of [BiI6] octahedra that share two opposite edges in such a fashion that two iodine atoms in cis-positions remain terminal. The calculated electronic structures and observed optical properties confirmed that compounds 1-4 are semiconductors with direct band gaps of 1.70-1.76 eV, which correspond to their intense red color. It was shown that the cations do not affect the optical properties, and the optical absorption is primarily associated with the charge transfer from the I 5p orbitals at the top of the valence band to the Bi 6p orbitals at the bottom of the conduction band. Based on their properties and facile synthesis, the title compounds are proposed as promising light-harvesting materials for all-solid solar cells.

We report the synthesis, crystal structures, and optical properties of two new compounds, K

The influence of auxiliary rare-earth element (REE) ions (M3+, M = Y, Gd, Tb) on the luminescence properties of the (EuxM1–x)2(BDC)3(H2O)4 (BDC2– = 1,4-benzenedicarboxylate) series was studied. The overall quantum yields (QYs) of the EuxM1–x series (M = Y, Gd; x > 0.05) appeared to be independent of both the ratio and the type of auxiliary metal ion. It is shown that M = Tb3+ does not cause luminescence enhancement.

The treatment of 5-(pyridine-2-yl-methyl)-2-thioxo-4-imidazolidinones with copper(II) chloride dihydrate led to the formation of a dinuclear copper complex L2Cu2Cl where L is a dehydrogenated initial organic ligand. X-ray diffraction analysis indicated that the starting 3,5-dihydro-4H-imidazole-4-ones undergo oxidation in the course of the reaction with the formation of an exocyclic double bond at C5 position.

We have synthesized and characterized a panel of new binuclear mixed valence Cu(I,II) complexes containing substituted 2-alkylthio-5-arylmethylene-4H-imidazolin-4-ones with unusual structure. These complexes are shown to be cytotoxic for various cell lines. We have found that these compounds did not intercalate DNA, inhibited number of polymerases (telomerase predominantly), accumulated in the cell nucleus, and caused DNA degradation. Preliminary studies revealed that lead compound inhibited human breast adenocarcinoma growth in mice model.

The treatment of 5-pyridylmethylene-substituted 2-thiohydantoins or 2-alkylthio-3,5-dihydro-4Н-imidazole-4-ones with CuCl2.2H2O affords the mononuclear or polymeric copper(II) complexes of the corresponding hydantoins. A presumable mechanism of hydantoin moiety formation involves Lewis acid catalyzed nucleophilic substitution of a sulfur-containing leaving group in the organic ligand by a water molecule from CuCl2.2H2O. The copper complexes Cu(L1-H)Cl(H2O) (7; L1 = (Z)-3-allyl-5-(pyridine-2-ylmethylene)imidazole-2,4(4H)-dione) and Cu(L2-H)2 (9; L2 = Z)-3-allyl-5-(5′-bromo-pyridine-2-ylmethylene)imidazole-2,4(4H)-dione) were characterized by X-ray diffraction.

The reactions of imidazolemethylene-substituted thiohydantoins with copper(II) chloride yield three kinds of complexes with different copper coordination mode. Binuclear complexes Cu2(L1-H)2Cl2 (5), Cu2(L2-H)2Cl (6) and polymeric complex [Cu(L2-H)Cl(H2O)]n (7) (L1 = (4Z)-2-thioxo-4-[(1-methyl-1H-imidazol-2-yl)methylene]-1-allylimidazol-5(4H)-one, L2 = (4Z)-2-thioxo-4-[(1-methyl-1H-imidazol-2-yl)methylene]-1-(n-propyl)imidazol-5(4H)-one) were synthesized and characterized by X-ray diffraction, IR and UV–Vis spectroscopy, and cyclic voltammetry. The crystal structures of homovalent dicopper(II,II) complex 5, mixed-valence [Cu+1.5, Cu+1.5] complex 6 and polymeric copper(II) complex 7 were refined from X-ray powder and single crystal data. Complexes 5–7 undergo eight-step quasi-reversible electrochemical reduction at +0.42 to −2.23 V to stable intermediates, which do not dissociate into free ligand and metal in the conditions of cyclic voltammetry experiments.

The crystal structure of 2-(4-methylphenyl)-2-oxo-1-(phenyliodonio)-1-(triphenylarsonio)ethanid tetrafluoroborate, C33H27AsIO+BF4 –, was solved and refined from laboratory X-ray powder diffraction data in combination with a DFT calculation (CoK α1, a=24.427(2) Å, b = 13.3412(18) Å, c=22.399(2) Å, β = 119.49(2)°, S.G. C2/c, R p/R wp = 0.030/0.039). The main features of the C33H27AsIO+BF4 – structure are similar to those reported previously for arsenium and phosphorous organic compounds. The distinctive features are short I … O and I … F (2.743(19) and 2.916(17) Å, respectively) intermolecular contacts, also observed previously in the same type of compound, refined from single crystal data.

The new tridentate organic N2S-type ligand, (4Z)-1-(2-azidoethyl)-4-[(pyridin-2-yl)-methylidene]-2-thioxoimidazol-5(4H)-one (LH), was synthesized. The reaction of LH with copper(II) chloride in a CH2Cl2/MeOH mixture afforded the coordination compound of the composition L2Cu2Cl (3). The crystal structure of 3 was solved and refined from X-ray powder diffraction data. Complex 3 has a binuclear structure with a short interatomic Cu-Cu distance and one bridging chlorine atom, which is located almost symmetrically with respect to both metal atoms. The planar organic ligands are noncoplanar and are at an angle of 53.56(1)° to each other.

Four iodobismuthates, LiBiI4·5H2O (1), MgBi2I8·8H2O (2), MnBi2I8·8H2O (3), and KBiI4·H2O (4), were prepared by a facile solution route and revealed thermal stability in air up to 120 °C. Crystal structures of compounds 1–4 were solved by a single crystal X-ray diffraction method. 1: space group C2/c, a = 12.535(2), b = 16.0294(18), c = 7.6214(9) A, β = 107.189(11)°, Z = 4, R = 0.029. 2: space group P21/c, a = 7.559(2), b = 13.1225(15), c = 13.927(4) A, β = 97.14(3)°, Z = 2, R = 0.031. 3: space group P21/c, a = 7.606(3), b = 13.137(3), c = 14.026(5) A, β = 97.14(3)°, Z = 2, R = 0.056. 4: space group P21/n, a = 7.9050(16), b = 7.7718(16), c = 18.233(4) A, β = 97.45(3)°, Z = 4, R = 0.043. All solid state structures feature one-dimensional (BiI4)− anionic chains built of [BiI6] octahedra that share two opposite edges in such a fashion that two iodine atoms in cis-positions remain terminal. The calculated electronic structures and observed optical properties confirmed that compounds 1–4 are semiconductors with...

During the polymorph screening of an active pharmaceutical ingredient tilorone dihydrochloride (chemical name 2,7-bis[2-(diethylamino)ethoxy]-9-fluorenone dihydrochloride) two new polymorphic modif...

The nucleophilic substitution in mixed phosphonium-iodonium ylides was investigated. The iodonium group is replaced by such S-containing nucleophiles as the thiocyanate anion or thiourea, as well as by halide ions. The structure of the reaction product with the thiocyanate ion was established by X-ray diffraction. A one-pot process involving the nucleophilic substitution and the Wittig reaction was developed.

The crystal structure of a complex molybdenum oxide Ag1/8Pr5/8MoO4 is reported. The Ag1/8Pr5/8MoO4 sub-structure can be described on the base of the scheelite (CaWO4) structure. Transmission electron microscopy reveals that the real structure is better described in a (3+1)D formalism. According to electron diffraction study the new scheelite-type complex oxide Ag1/8Pr5/8MoO4 crystallizes in the B2/b(αβ0)00 (3+1)D superspace group with unit cell parameters a ≈ 7.5 0 A , b ≈ 5.3 0 A , c ≈ 1 1.7 4 A and γ ≈ 1 3 5 ° ( Z = 4 ) and modulation vector q = 0.5 6 a * + 0.5 9 b * . The structure of Ag1/8Pr5/8MoO4 is refined from X-ray powder data in the scheelite setting I2/b(αβ0) with a = b = 5.3 0 1 3 ( 4 ) A , c = 1 1.7 4 0 7 ( 1 1 ) A , q = 1.1 4 6 9 0 ( 1 4 ) a * + 0.5 8 9 2 1 ( 1 2 ) b * with fixed γ = 9 0 ° angle ( R p = 0.0 3 3 , R = 0.0 3 3 , R m = 0.0 2 9 , R 1 = 0.0 4 7 , S = 1.3 6 ). Displacement modulations apply for all atoms. The occupancy modulation shows that one-fourth of the Ag/Pr atoms are absent. The structure can be considered as a crystallographic shear structure with incommensurate ordering of vacancies and displacement modulations for all atoms. The arrangement of Ag/Pr atoms and vacancies is at the origin of the incommensurate modulation in the cation-deficient Ag1/8Pr5/8MoO4 phase.

Single crystals of MgB2 with a size up to 1.5x0.9x0.2 mm3 have been grown with a high pressure cubic anvil technique. The crystal growth process is very peculiar and involves an intermediate nitride, namely MgNB9. Single crystals of BN and MgB2 grow simultaneously by a peritectic decomposition of MgNB9. Magnetic measurements in fields of 1-5 Oe show sharp transitions to the superconducting state at 37-38.6 K with width of ~0.5 K. The high quality of the crystals allowed the accurate determination of magnetic, transport and optical properties as well as scanning tunnelling spectroscopy (STS) and decoration studies. Investigations of crystals with torque magnetometry show that Hc2//c is very low (24 kOe at 15 K), while Hc2//ab increases up to 140 kOe at 15 K. The upper critical field anisotropy gamma = Hc2//ab/ Hc2//c was found to be temperature dependent (decreasing from 6 at 15 K to 2.8 at 35 K). The effective anisotropy gamma_eff, as calculated from reversible torque data near Tc, is field dependent (increasing roughly linearly from 2 in zero field to 3.7 in 10 kOe). The temperature and field dependence of the anisotropy can be related to the double gap structure of MgB2 with a large two-dimensional gap and small three-dimensional gap, the latter being rapidly suppressed in a magnetic field. Torque magnetometry investigations show a pronounced peak effect, indicating an order-disorder transition of vortex matter. Decoration experiments and STS visualise a hexagonal vortex lattice. STS spectra evidence two gaps (3 meV/6 meV) with direction dependent weight. Magneto-optic investigations with H//c show a clear signature of the smaller of the two gaps, disappearing in fields higher than Hc2//c.

A new monohydrate of lithium perrhenate LiReO 4 ·H 2 O was prepared by dehydration of LiReO 4 ·1.5H 2 O at room temperature. The single crystals of LiReO 4 ·H 2 O were obtained by crystallisation from the isoamyl acetate solution of LiReO 4 ·1.5H 2 O. The structure of monohydrate ( a =5.6674(4), b =10.771(1), c =7.4738(7) A, β =102.422(7)°, R 1 =0.0414, space group P 2 1 / a , Z =4) is built up from LiO 3 (H 2 O) 2 trigonal bipyramids and ReO 4 tetrahedra sharing common edges and corners inside the layers. The layers are connected together by hydrogen bonds. The relationships between the structures of sesquihydrate, monohydrate and anhydrous LiReO 4 are discussed.

The structure of the cation-deficient Ba4.0(1)Ce0.98(3)Nb10O30 barium cerium reduced niobate with a tetragonal tungsten bronze (TTB) type structure was refined from X-ray single crystal data (tetragonal, a=12.508(2) A, c=3.9328(4) A, S. G. P4/mbm, Z=1, R=0.019, Rw=0.023). It was found that rare earth substitution for Ba is accompanied by formation of vacancies in A sites. Vacancies were preferably formed in the A(1) cavities in the structure.

Exact mapping of gene starts is an important problem in the computer-assisted functional analysis of newly sequenced prokaryotic genomes. We describe an algorithm for finding ribosomal binding sites without a learning sample. This algorithm is particularly useful for analysis of genomes with little or no experimentally mapped genes. There is a clear correlation between the ribosomal binding site (RBS) properties of a given genome and the potential gene start prediction accuracy. This correlation is of considerable predictive power and may be useful for estimating the expected success of future genome analysis efforts. We also demonstrate that the RBS properties depend on the phylogenetic position of a genome.

The oxazole fragment is involved as a structural unit in some biologically active compounds. A large number of oxazole containing compounds were isolated from vari ous natural sources, particularly, of the sea origin. Many of these compounds exhibit different activities, for example, antiviral, antifungal, and antibacterial activities.1,2 An analysis of the published data shows that there are no general approaches to the synthesis of 2,4 and 2,4,5 substituted oxazoles.3—5 Iodonium ylides hold prom ise as reagents for the synthesis of oxazoles.6,7 Recently, we have found that mixed phosphonium iodonium ylides 1 have different reactivities associated primarily with the existence of the enolate resonance form.8—10 An analysis of the structural features of ylide suggests that this compound can be used as a 1,3 dipole in the synthesis of furans 2 according to Scheme 1.

The crystal structure of the new complex vanadium oxide Na(6)Mg(2)(VO(4))(2)(V(2)O(7)) was solved from X-ray single-crystal data. The structure contains VO(4) tetrahedra and MgO(6) octahedra, linked by corners and forming a complex three-dimensional framework. A half of the VO(4) tetrahedra are connected only to MgO(6) octahedra, whereas the others are corner-sharing, forming V(2)O(7) pyrovanadate groups with statistically random orientations. One unique Mg atom is located at an inversion centre, while the other Mg atom, one unique V atom and five unique O atoms lie on mirror planes.

The incommensurately modulated structure of Bi2Sr2Eu1.3Ce0.7Cu2O10.17, with a = 5.4752(4) Å, b = 5.4522(3) Å, c = 17.860(1) Å, Z = 2, was refined by the GJANA program [Gao et al., Acta Cryst. A 49, 141 (1993)] from X-ray powder data in C:C2mb: 111 four-dimensional space group (Rov = 0.064, Rm = 0.041, Rsat = 0.202, Rp = 0.049, Rwp = 0.065). Displacive modulation parameters of all cations and oxygen atoms in the Bi-layer were involved in the refinement. Obtained results including the modulation parameters are in agreement with those found for the similar phase Bi2Sr1.7Nd1.8Ce0.5Cu2O10+δ from single-crystal data [Mironov et al., J. Solid State Chem. 109, 74 (1994)].

Pre-mRNA structure impacts many cellular processes, including splicing in genes associated with disease. The contemporary paradigm of RNA structure prediction is biased toward secondary structures that occur within short ranges of pre-mRNA, although long-range base-pairings are known to be at least as important. Recently, we developed an efficient method for detecting conserved RNA structures on the genome-wide scale, one that does not require multiple sequence alignments and works equally well for the detection of local and long-range base-pairings. Using an enhanced method that detects base-pairings at all possible combinations of splice sites within each gene, we report a list of RNA structures that could be involved in the regulation of splicing in mammals. We demonstrate statistically that there is a strong association between the occurrence of conserved RNA structures and alternative splicing, where local RNA structures are generally more frequent at alternative donor splice sites, while long-range structures are more associated with weak alternative acceptor splice sites. A fraction of the reported structures is associated with unannotated splicing events that are confirmed by RNA-seq data. As an example, we validated the RNA structure in the human SF1 gene using mini-genes in the HEK293 cell line. Point mutations that disrupted the base-pairing of two complementary boxes between exons 9 and 10 of this gene altered the splicing pattern, while the compensatory mutations that reestablished the base-pairing reverted splicing to that of the wild-type. There is statistical evidence for a Dscam-like class of mammalian genes, in which mutually exclusive RNA structures control mutually exclusive alternative splicing. In sum, we propose that long-range base-pairings carry an important, yet unconsidered part of the splicing code, and that, even by modest estimates, there must be thousands of such potentially regulatory structures conserved throughout the evolutionary history of mammals.

Crystal structures of Nd 1+ x Ba 2− x Cu 3 O 7−δ phase ( x =0.05, 0.22 and 0.42) were refined from X-ray single-crystal data (tetragonal system, space group P4/mmm, Z =1, R =0.027, 0.027, 0.025 respectively). The main differences between these similar structures deal with the cation and oxygen sites in the (Ba/NdO) layer. Joint occupation of the same site by Ba and Nd ions with essentially different ionic radii results in the splitting of that site along the c -axis and the shift of the oxygen in this layer from the ideal position at the four-fold axis to achieve appropriate coordination for the smaller rare earth cation. These changes may be the structural reason for the suppression of superconductivity in R 1+ x Ba 2− x Cu 3 O 7−δ (R is rare earth) phases.

A single crystal of Bi 2 Sr 1.7 Nd 1.8 Ce 0.5 Cu 2 O 10+δ (2222 phase) was obtained and its structure refined, including parameters describing the structural modulation (orthorhombic system, four-dimensional space group C:C2mb: 111, a = 5.5000(4) A, b = 5.4846(7) A, c = 17.873 A, Z = 2). The refinement of the average structure gave R = 0.061, while structure refinement including displacive and thermal modulation parameters resulted in R = 0.042 (overall) and R = 0.030 for the main reflections. The amplitudes and directions of modulation are very similar to those in the 2212 phase (1, 2), with displacements ranging up to 0.4 A. The refinement shows extra oxygen to be located in BiO layers, and gives δ = 0.32(8), in reasonable agreement with previously reported values.

Pre-mRNA structure impacts many cellular processes, including splicing in genes associated with disease. The contemporary paradigm of RNA structure prediction is biased toward secondary structures that occur within short ranges of pre-mRNA, although long-range base-pairings are known to be at least as important. Recently, we developed an efficient method for detecting conserved RNA structures on the genome-wide scale, one that does not require multiple sequence alignments and works equally well for the detection of local and long-range base-pairings. Using an enhanced method that detects base-pairings at all possible combinations of splice sites within each gene, we now report RNA structures that could be involved in the regulation of splicing in mammals. Statistically, we demonstrate strong association between the occurrence of conserved RNA structures and alternative splicing, where local RNA structures are generally more frequent at alternative donor splice sites, while long-range structures are more associated with weak alternative acceptor splice sites. As an example, we validated the RNA structure in the human SF1 gene using minigenes in the HEK293 cell line. Point mutations that disrupted the base-pairing of two complementary boxes between exons 9 and 10 of this gene altered the splicing pattern, while the compensatory mutations that reestablished the base-pairing reverted splicing to that of the wild-type. There is statistical evidence for a Dscam-like class of mammalian genes, in which mutually exclusive RNA structures control mutually exclusive alternative splicing. In sum, we propose that long-range base-pairings carry an important, yet unconsidered part of the splicing code, and that, even by modest estimates, there must be thousands of such potentially regulatory structures conserved throughout the evolutionary history of mammals.

A new monohydrate of lithium perrhenate LiReO 4 ·H 2 O was prepared by dehydration of LiReO 4 ·1.5H 2 O at room temperature. The single crystals of LiReO 4 ·H 2 O were obtained by crystallisation from the isoamyl acetate solution of LiReO 4 ·1.5H 2 O. The structure of monohydrate ( a =5.6674(4), b =10.771(1), c =7.4738(7) A, β =102.422(7)°, R 1 =0.0414, space group P 2 1 / a , Z =4) is built up from LiO 3 (H 2 O) 2 trigonal bipyramids and ReO 4 tetrahedra sharing common edges and corners inside the layers. The layers are connected together by hydrogen bonds. The relationships between the structures of sesquihydrate, monohydrate and anhydrous LiReO 4 are discussed.

The structure of a new magnesium nitridoboride, MgNB9, has been refined from single-crystal X-ray data. The Mg and N atoms lie on sites with crystallographic 3m symmetry. The structure consists of two layers alternating along the c axis. The NB6 layer, with B12 icosahedra, has the C2B13 structure type. Within this layer, boron icosahedra are bonded to N atoms, each coordinating to three boron polyhedra. Another MgB3 layer, with B6 octahedra, does not belong to any known structure type. The boron icosahedra and octahedra are connected to each other, thus forming a three-dimensional boron framework.

The oxazole fragment is involved as a structural unit in some biologically active compounds. A large number of oxazole containing compounds were isolated from vari ous natural sources, particularly, of the sea origin. Many of these compounds exhibit different activities, for example, antiviral, antifungal, and antibacterial activities.1,2 An analysis of the published data shows that there are no general approaches to the synthesis of 2,4 and 2,4,5 substituted oxazoles.3—5 Iodonium ylides hold prom ise as reagents for the synthesis of oxazoles.6,7 Recently, we have found that mixed phosphonium iodonium ylides 1 have different reactivities associated primarily with the existence of the enolate resonance form.8—10 An analysis of the structural features of ylide suggests that this compound can be used as a 1,3 dipole in the synthesis of furans 2 according to Scheme 1.

The nucleophilic substitution in mixed phosphonium-iodonium ylides was investigated. The iodonium group is replaced by such S-containing nucleophiles as the thiocyanate anion or thiourea, as well as by halide ions. The structure of the reaction product with the thiocyanate ion was established by X-ray diffraction. A one-pot process involving the nucleophilic substitution and the Wittig reaction was developed.

The crystal structure of a new high-pressure modification of cadmium divanadium hexa­oxide, CdV2O6, was refined from X-ray single-crystal data. It contains zigzag chains of edge-sharing VO6 octa­hedra. Octa­hedra in adjacent chains share corners and form corrugated layers. Octa­hedrally coordinated Cd atoms, which lie on twofold axes, are situated between the layers. The columbite-like structure results in a strong distortion of the CdO6 octa­hedra which may be stabilized only at high pressure.

The crystal structure of a new high-pressure modification of cadmium divanadium hexaoxide, CdV(2)O(6), was refined from X-ray single-crystal data. It contains zigzag chains of edge-sharing VO(6) octahedra. Octahedra in adjacent chains share corners and form corrugated layers. Octahedrally coordinated Cd atoms, which lie on twofold axes, are situated between the layers. The columbite-like structure results in a strong distortion of the CdO(6) octahedra which may be stabilized only at high pressure.

The crystal structure of the new complex vanadium oxide Na(6)Mg(2)(VO(4))(2)(V(2)O(7)) was solved from X-ray single-crystal data. The structure contains VO(4) tetrahedra and MgO(6) octahedra, linked by corners and forming a complex three-dimensional framework. A half of the VO(4) tetrahedra are connected only to MgO(6) octahedra, whereas the others are corner-sharing, forming V(2)O(7) pyrovanadate groups with statistically random orientations. One unique Mg atom is located at an inversion centre, while the other Mg atom, one unique V atom and five unique O atoms lie on mirror planes.